A nice aluminium case is available on the Pine64 store listed as "ROCKPro64 PREMIUM ALUMINUM CASING".
The Quartz64 model A can be made to fit this case, however some filing of one of the holes is necessary because one of the RockPro64 ports is a type-C, whereas on the Quartz64 model A all of the ports are type As.
Interference between Quartz64 model A and the case as supplied:-
Fitment once the case has been filed:-
Fitment of the other end (no modification necessary):-
Also note that the SoC in the Quartz64-A is slightly lower than the Rock64 Pro one (apparently about 0.6mm). This case includes an internal post which (using a thermal pad) touches the SoC to transfer heat from the SoC to the case. However it does not make good contact with the RK3566. The best solution is probably to source a thicker thermal pad.